Various designs of vacuum cups have been utilized to retain and secure a workpiece by applying negative air pressure or vacuum between the vacuum cup and the workpiece. Typically, the vacuum cup is secured to a manipulator or transfer boom which moves the vacuum cup thereby imparting motion to a vacuum cup engaged workpiece. The use of the vacuum cup allows the workpiece to be picked up and transferred while avoiding the use of any type of mechanical components directly contacting the workpiece. Such mechanical components can impose harmful forces on the workpiece thereby resulting in flawing or damaging the workpiece and surfaces thereof.
When the workpiece consists of thin sheet metal, certain vacuum cup designs may impart too much vacuum on the sheet metal workpiece thereby causing a phenomenon called "tin cupping". Tin cupping occurs when a portion of the sheet metal workpiece deforms or "bubbles up" from the force of the vacuum created by the vacuum cup. Such tin cupping may create flaws or deformations in the surface of the sheet metal which are undesirable.
In addition, such sheet metal workpieces may collect oils and residues on the surface of the sheet metal which are typical of the machining and industrial environments in which they are created. Such oils and residues can create a hydroplaning effect between the vacuum cup and the workpiece thereby affecting the retention of the workpiece by the vacuum cup.
Thus, it is desirable to produce a vacuum cup apparatus that avoids the tin cupping phenomena associated with most sheet metal workpieces. In addition, it is also desirable to create a vacuum cup apparatus that displaces any oils or residues which may be found on the sheet metal workpiece and that may affect the retention of the sheet metal workpiece by the vacuum cup apparatus.